1. Field of the Invention
The present invention relates to a variable valve unit for an internal combustion engine, which can vary a drive phase of an intake or exhaust value.
2. Description of the Related Art
Most engines built for automobiles are equipped with a variable valve unit to restrict exhaust gas of an engine and to reduce fuel consumption (gas mileage). The variable valve unit changes a phase, that is, open and close timing of intake/exhaust valve in accordance with driving mode of automobiles.
A reciprocating cam structure is given as the structure of the variable valve unit. According to the reciprocating cam structure, a phase of cam formed in a camshaft is temporarily replaced with a reciprocating cam. The reciprocating cam has a base circle interval and a lift interval, which communicate with each other.
In this kind of reciprocating cam structure, a rocker arm mechanism is often used to vary a ratio of a base circle interval and a lift interval replaced with the reciprocating cam. The rocker arm mechanism changes the foregoing ratio in accordance with driving mode of automobiles. For example, Japanese Patent No. 3245492 discloses the variable valve unit described above.
In the variable valve unit disclosed in the foregoing Japanese Patent No. 3245492, components of the variable valve unit are attached to a cylinder head in order.
When assembling these components of the variable valve unit into the cylinder head, there is a possibility that an assembly error occurs. The assembly error is a factor of generating a difference in each valve lift and valve opening timing. If the difference occurs in valve lift and valve opening timing, a difference occurs in combustion state of each cylinder. The difference of combustion state of each cylinder is a factor of generating vibration and worsening gas mileage (fuel consumption).
The variable valve unit disclosed in the foregoing Japanese Patent No. 3245492 is hard to adjust the assembly error in the variable valve unit.